FIELD OF THE INVENTION
The invention relates to a winding element for an electrical machine, having an electrically conductive conductor configuration for carrying an electric current, an insulating layer which surrounds the conductor configuration and a protective configuration which surrounds the insulating layer and has an isolating layer. The invention also relates to an assembly and a set having a plurality of such winding elements.
Published International Patent Application WO 91/01059 A1 corresponding to U.S. Pat. No. 5,030,870, as well as Published International Patent Application WO 93/06646 A1, disclose a winding element of a known type and notes relating to a combination of such a winding element with identical winding elements to form a set, wherein the winding elements are connected to one another and form a winding for an electrical machine, specifically a turbogenerator. The protective configuration in such a winding element is used to compensate for mechanical expansion, which results when the winding element is subjected to changing temperatures. The protective configuration forms an electrically screened zone in the isolating layer. The electrically screened zone surrounds the conductor configuration and the insulating layer and has a strength which is considerably less than the strength of the insulating layer and the strength of the conductor configuration. Thus, when expansion occurs, the expansion can be compensated for by gaps which are formed in the isolating layer. As stated, each of those gaps is electrically screened. For that reason, it is not possible for any corona discharge to form in the gap, which could damage the winding element. The electrical screening of the isolating layer is formed by using electrically conductive textiles, in particular woven or non-woven fabrics, which enclose between them the isolating layer that contains flakes of mica splittings as effective components. The electrically conductive textiles may be textiles made of electrically conductive fibers, in particular certain plastic fibers, and they may also be made of electrically insulating fibers, for example glass fibers, and be made electrically conductive subsequently by the addition of further components, for example electrically conductive coatings and/or soot. In order to ensure the electrical screening of the isolating layer, the electrically conductive contact layers or bridges which enclose it and run through the isolating layer make contact with one another electrically. Those bridges are formed by a further textile strip, which is at least slightly electrically conductive. The isolating layer itself is prepared as a strip which contains the flakes of mica splittings. The flakes of mica splittings tend to split further and it is that tendency on which the reduced strength of the isolating layer and the formation of gaps during a mechanical expansion process are based. The strip is wound onto the winding elements and another electrically conductive strip, which forms the bridges, is passed alternately over the mica strip or under the mica strip, forming the necessary bridges. The bridges are those sections of the strip which come to rest between two layers, that are located next to one another, of the strip which contains the flakes of mica splittings, and thus extend from an inner side which faces the insulating layer, to an outer side which faces away from the insulating layer, of the strip that contains the mica splittings. The contact layers may be fitted separately from the isolating layer or together with the isolating layer. In particular, one of the contact layers may be a textile carrier material for the flakes of mica splittings.
An important constituent of the insulating components of a winding element for an electrical machine is a resin preparation, into which further constituents of the insulating components, in particular mica preparations, are incorporated. According to normal practice, the mica preparations are contained in strips which are wound onto the conductor configuration of the winding element and are subsequently impregnated with the resin preparation. The resin preparation is initially liquid and viscous and, after it has been introduced into the insulating components, is cured by initiating a specific chemical process. The use of a resin preparation in the form of a mixture of an epoxy resin and an anhydride of an organic acid is normal. The resin preparation is cured by initiating a specific chemical reaction which leads to chemical bonding of the anhydride to the epoxy resin and, in doing so, becomes a solid body. The impregnation and curing can be carried out separately for each winding element. It is also possible, as well as advantageous, for an electrical machine of a size that is normal for electrical machines having power outputs or power consumptions up to 300 MW, to have all of the winding elements initially connected to form the complete winding without prior impregnation and for the winding to be subsequently impregnated with the resin preparation together with a winding support on which it is installed, and for the resin preparation to be cured. That method is known as the "entire impregnation method".
Materials which are in the form of strips, are electrically conductive to a greater or lesser extent and can be used for corona protective configurations on winding elements, as known from German Published, Prosecuted Patent Applications DE-AS 1 021 062 and DE-AS 11 18 290 and Swiss Patent CH-PS 521 661. However, none of those documents refer to the use of such material in the form of a strip in conjunction with an isolating layer, as explained above.
A disadvantage of the winding elements which are known from Published International Patent Application WO 91/01059 A1 corresponding to U.S. Pat. No. 5,030,870 and which are known from Published International Patent Application Wo 93/06646 A1, can result from the fact that the application of the isolating layer with the necessary electrically conductive bridges is relatively complicated and consequently as a rule has to be carried out by manual work.